Grading out 49ers’ 45-3 rout of the Bills

Here is how the 49ers graded out from their 45-3 win Sunday over the visiting Buffalo Bills:

Pass offense

Alex Smith sparked the biggest yardage day in 49ers history (621 total yards). Now the NFL’s leader in passer rating (108.7), Smith passed for 237 of his 303 yards before halftime. Michael Crabtree, Mario Manningham and Kyle Williams made touchdown catches look easy. The 49ers are stretching the field more, protecting Smith better and gaining more yards after the catch.

Grade: A

Run offense

In a historic display of balanced offense, the 49ers were the first team to complement a 300-yard passing day with a 300-yard rushing attack. They ran for 228 of their 311 yards after halftime. Frank Gore hit the century mark (106 yards, plus a TD), Kendall Hunter ran for a career-high 81 yards and Anthony Dixon scored. Another 88 yards came from their quarterbacks’ legs, including 39 yards and a TD from Colin “WildKap” Kaepernick. Kudos to Delanie Walker for sticking out in a dominant blocking display.

Grade: A

Pass defense

The 49ers are allowing only 181. 2 passing yards per game, the second-best mark behind only the Dallas Cowboys (169.5). The pass rush may not be finishing with sacks — Ahmad Brooks had the only one Sunday — but an imposing force still exists in Justin Smith (no sacks in 2012).

Grade: A

Run defense

No opponent has scored a rushing touchdown in the past 12 regular-season games at Candlestick. Patrick Willis (forced fumble) and NaVorro Bowman look in sync, and next up for them is the Giants’ Ahmad Bradshaw, who ran for 200 yards Sunday against the Browns.

Grade: A

Pass defense

The 49ers didn’t allow any completion longer than 20 yards. Chris Culliver saw a lot of time in the nickel package and came through with his first interception this season.

Grade: A

Special teams

Coverage units have been exposed as the 49ers’ biggest flaw. While a holding call rightfully nullified a Bills touchdown on an 80-yard punt return, the 49ers allowed a 59-yard kickoff return the next time Leodis McKelvin touched the ball. David Akers tied a franchise record by making a field goal in his 21st consecutive game.

Grade: C

Coaching

Once sought by the Bills to become their coach, Jim Harbaugh deflected all credit to his players and assistants. Offensive coordinator Greg Roman called a masterful game and bolstered his stock of becoming a head coach by Valentine’s Day, if not sooner.